select sum(t.prix * a.nb_prest)
from PRESTATION p , TARIF t , ACHAT a , TICKET ti , USAGER u
where type_prest="supplement chantilly"
and p.num_prest=t.num_prest
and t.num_prest=a.num_prest
and a.num_ticket=ti.num_ticket
and ti.num_carte =u.num_carte
and u.num_categ=t.num_categ